The allergies themselves should not be contagious. But there are other issues to regard. When there is a problem with the air conditioning or the air is not clean people with allergies or airway problems will notice it sooner, but you could be affected also (in a lesser degree).
Also allergies can change with age, I have problems with certain substances in the air but the degree of sensitivity changed with my age. During early childhood it was at its top, then minimal and resurfaced around the age of seventeen.
There could also be contagious diseases like the common cold, but that one cannot be avoided most of the times.
The best thing to do is keep your office well ventilated, open windows etc and go for a outside walk some time during the day.